This invention relates in general to vehicle vacuum brake boosters, and in particular to the manufacturing of input rods and output rods for vacuum boosters.
U.S. Pat. No. 5,493,946, which is incorporated by reference herein, discloses a known vehicle vacuum brake booster. The FIGS. 1-3 are representative of drawings from U.S. Pat. No. 5,493,946 and will be used herein to describe an example of a brake booster to which an input rod, as manufactured by various methods described herein, may be used in place of a conventionally known solid input rod shown in FIGS. 1-3.
The brake booster illustrated in FIGS. 1 to 3 is substantially rotationally symmetrical with reference to an axis A which normally agrees with the longitudinal direction of the vehicle when installed in a motor vehicle. As shown in FIG. 1 the brake booster is of tandem design having a booster housing 10, a first chamber 12 and a second chamber 14, which are separated from each other by a movable wall 16, as well as a first additional chamber 12′ and a second additional chamber 14′, which are separated from each other by a movable wall 16′. The booster housing 10 is held together by a parallel-axis arrangement of tension rods 18, of which only one is illustrated. There is no need to detail special features resulting from the tandem design, since these are known; it being sufficient to comment that the first chamber 12 is permanently connected to the first additional chamber 12′, and the second chamber 14 is permanently connected to the second additional chamber 14′.
Associated with the brake booster is a control valve 20 which is incorporated in the main in the booster housing 10 and has with reference thereto an axially movable valve body 22. In the interior of the valve body 22 an annular first valve seat 24 is formed which separates a passage 26 merging into the rear chamber 12 from a passage 28 merging into the front chamber 14. The valve body 22 has further an axial bore in which a central sleeve 29 is disposed secured to the valve body 22. In the axial bore and on the sleeve 29 a sleeve-shaped valve barrel 30 is slidingly guided along the axis A. The valve barrel 30 is composed of front and rear components which are bolted together as shown in FIG. 1. At the rear end of the rear component (shown on the right in the drawing) of the valve barrel 30 a second valve seat 32 is formed concentric to the first valve seat 24.
Spaced upstream from the second valve seat 32 (shown on the left in the drawing) the valve barrel 30 has a radial recess 34 which joins another radial recess 36 configured wider, however, in the axial direction in the valve body 22. The valve barrel 30 is permanently urged to the rear (to the right in FIGS. 1 to 3) by an axially preloaded valve spring 38. In the control valve 20 a solenoid 40 is incorporated which is assigned to the left-hand component of the valve barrel 30 as the solenoid armature such that the valve barrel 30 is drawn forwards against the resistance of the valve spring 38 when the solenoid 40 is energized.
In the central sleeve 29 a piston rod 41 of a piston 42 is guided which at its rear end is connected to the rod-shaped actuating element 44 (or input rod) and having at its front end a piston head 46. The latter forms together with a rubber element 48 embedded in the valve body 22 and a booster output member 50 arranged in front thereof, a mechanical force translation means of the usual kind in brake boosters.
The other end of the input rod or actuating element 44 is pivotally connected to a brake pedal linkage 11, schematically illustrated in FIG. 1. The linkage includes a member 11a which is pivotally connected to portion of the vehicle 11b (such as the frame or the instrument panel of the vehicle). The actuating element 44 is also pivotally connected to the member 11a at a pivot 11c. A brake pedal 11d is attached to an end of the member 11a and is depressed by the foot of the driver of the vehicle. Of course, the linkage 11 may include any number of members 11a in any suitable connecting arrangement. A force acting on the brake pedal 11d by the driver's foot is transmitting through the member 11a causing leftward movement of the actuating element 44 to actuate the brake booster and associated master cylinder (not shown). The end 44a of the actuating element (or input rods a described below) may have a spherical shape and be received in a socket 42a of the piston 42 for a pivoting connection to accommodate slight vertical and/or lateral movement of the actuating element 44 as the actuating element 44 is moved longitudinally (leftward) during actuation.
The actuating element 44 (input rod) generally includes a forward end (left-hand end as viewing FIG. 1) which is generally cylindrical or annular in shape. The actuating member 44 includes a shoulder 44b formed therein for providing a stop for a spring 58. The other end (right-hand end as viewing FIG. 1) of the actuating element 44 includes a yoke structure for pivotally connecting to the brake pedal linkage member 11a. The yoke structure includes a pair of laterally spaced flanges 44c. This arrangement is referred to as a clevis-type design. The yoke structure of the actuating element 44 includes openings 44d formed therein to receive a pivot pin (not shown) pivotally connected the member 11a to the actuating member 44.
In an annual groove of the piston 42 a stopper element 52 is latched in such a way that it is connected to the piston for common axial movement. The stopper element 52 extends radially outwards through the recesses 34 and 36 in the valve barrel 30 and valve body 22 respectively and in the illustrated rest position of the piston 42 is in contact with a stopper 53 which is formed on a shoulder of the booster housing 10 and is thus independent of the position of the valve body 22.
Spaced away from the rear of the stopper element 52 a flange-like coupling element 54 is formed which in the illustrated rest position of the piston 42 and of the valve barrel 30 is in contact with an annular abutment 55 formed on the valve barrel. The valve spring 38, resulting in this contact, is totally disposed within the valve barrel 30 and tensioned between the second valve seat 32 and the piston 42.
Radially outwards from the abutment 55 an annular seal 56 is disposed, located in an annular recess 57 formed open to the rear end in the piston 42 and which in the illustrated rest position seals off the coupling element 54 of the piston 42. The effective diameter of the seal 56 is, as shown in FIGS. 1 to 3, slightly smaller than the effective diameter of the second valve seat 32. The region downstream of the seal 56 (on the right in the drawing) is continuously exposed to atmospheric pressure. In the illustrated rest position of the valve barrel 30 the seal 56 prevents the atmosphere from gaining access to the rear chamber 12 via the valve barrel 30 and the recesses 34 and 36.
By means of a rear return spring 58 the actuator element 44 (input rod) is normally maintained in its illustrated rest position in which an annular sealing element 60 disposed within the valve body 22 in the usual way and pretensioned forwardly by a spring 62 has sealing contact with the first valve seat 24, while not providing a total seal of the second valve seat 32, a slight difference in pressure existing between the two chambers 12 and 14. In operation the front chamber 14 is permanently connected to a vacuum source, as a result of which a vacuum exists in both chambers 12 and 14 in the rest position of the valve barrel 30. The moving wall 16 and the valve body 22 connected thereto in common axial movement thereof are urged into their rear final position, as shown, by a front return spring 64.
In idle condition the stopper element 52 is in contact with the stop 53, thereby defining the rest position of the piston 42. The valve barrel 30 is supported by the coupling member 54 with practically all of the force exerted by the valve spring 38 clamped between the valve barrel and the piston 42, thereby also defining the rest position of the valve barrel 30, the second valve seat 32 being maintained in contact with the sealing element 60 by a slight residual force of the valve spring 38.
On forward displacement of the actuator element 44 via the pedal linkage 11, which for instance is connected to the brake pedal of a vehicle, thus producing forward displacement of the piston 42, the coupling member 54 thereof includes displacement of the abutment 55 and thus of the valve barrel 30 as a whole so that its valve seat 32 is released from the sealing element 60, allowing the downstream flow of atmosphere into the valve body 22 to access the rear chamber 12 through the passage 26 and further through the radial recess 36 in the valve body 22. The front chamber 14 is separated from the rear chamber 12, since the sealing element 60 is maintained firmly in contact with the first valve seat 24, thereby resulting in a difference in pressure between the two chambers 12 and 14 which causes the movable wall 16 together with the valve body 22 and the booster output member 50 to be displaced forwardly. The booster output member 50 transfers the force acting on it to a brake master cylinder 66, the rear end area of which is illustrated in FIG. 1.
If the forward movement of the valve barrel 30, affected mechanically via the piston 42, and the attendant booster output to the brake master cylinder 66 need to be accelerated and amplified, the solenoid 40 is energized so that it draws the valve barrel 30 away from the coupling element 54 forwards, thereby increasing the clear flow cross-section between the second valve seat 32 and the sealing element 60. Such a boosted output of the brake booster may for instance be desirable when the vehicle being decelerated is heavily loaded or when particularly fast forward movement of the actuator element 44 indicates that braking action is wanted on an emergency.
In these instances the solenoid 40 receives current via a controller with which an acceleration sensor monitoring the actuator element 44 is associated. Instead of this or additionally the power supply of the solenoid 40 may be controlled by a distance sensor which triggers braking action without the driver of the motor vehicle being involved, when the distance away of a vehicle driving ahead violates a specific minimum. In the latter case the control causes, via the solenoid 40, to be moved forward, thus allowing an inflow of atmosphere into the first chamber, even in the absence of a mechanical actuation, i.e. the piston 42 remaining in its rest position.
In any case, on de-energization of the solenoid 40 the valve barrel 30 is again urged rearwards by the valve spring 38 so that the abutment 55 is returned in contact with the coupling element 54 and the seal 56 is again effective. On completion of a mechanical force input via the actuator element 44 the piston 42 together with the valve barrel 30 returns to the rest position. The movable wall 16 and the valve body 22 fail to be involved in this return movement as long as a difference in pressure exists between the chambers 12 and 14. This difference in pressure is depleted by the valve barrel 30 urging the sealing element 60 a short distance to the rear so that it unseats from the first valve seat 24.
Previously known input rods, such as the actuator element 44 shown in FIGS. 1-3, generally include a body portion 44′ and a connecting portion 44″. The body portion 44′ is generally elongate and is disposed in the vacuum booster. The body portion 44′ has an annular shape and is formed from a solid stock of material, and more particularly, a solid round bar. The bar is formed and machined, such on a lathe or other cutting tool, to form the annular shape. The machining operation forms the spherical end 44a and a tapered portion 44e extending rearwardly from the spherical end 44a. The body portion 44′ also includes a shoulder 44d formed therein which may function as spring stops. The connecting portion 44″ includes features for pivotally connecting the actuator element 44 to the pedal linkage 11. The connecting portion may be in the form of a clevis-type design, such as shown in FIG. 1, having a pair of spaced apart flanges 44c. Other known connecting portions include a paddle style in which a single flattened plate shaped end (instead of two flanges 44c) is used to provide a connection to the pedal linkage 11.